Air blast circuit breakers



A. LATOUR AIR BLAST CIRCUIT BREAKERS Dec. 29, 1959 2 Sheets-Sheet 1 Filed June 28, 1957 m a m a 1, m 0 0 m m L w E III I Q/O/ Z// 7/ 7 54 w 37 2 I'll. I| M a? f N 6 9 Fig. 4-

Dec. 29, 1959 A. LATOUR AIR BLAST CIRCUIT BREAKERS Filed June 28,1957

2 Sheets-Sheet 2 H, T. uv 1 ANDRE 1.47 0 2 United States Patent AIR BLAST CIRCUIT BREAKERS Andre Latour, Grenoble, France, assignor to Etablissements Merlin & Gerin, Grenoble, France Application June 28, 1957, Serial No. 668,687

Claims priority, application France July 10, 1956 Claims. (Cl. 200-148) This invention pertains to electrical circuit breakers, and especially to heavy current circuit breakers of the air blast type in which the compressed air used for the air blast to improve the extinguishing of the arc, is also employed to provide very positive and quick opening of the circuit breaker.

It is an important object of the invention to provide an improved electrical circuit breaker of the above type in which the admission of compressed air to the extinction chamber (hereinafter called simply the chamber), initially and prior to the opening of the contacts, provides a temporary increase of the contact pressure and operates to prevent their opening prematurely; that is, untilthe full are extinction pressure has been built up in the chamber.

Another'object of the invention is to provide a circuit breaker of the above type in which the motion of the movable contact is damped, near the end of its openingtravel, for smooth and efiicient operation and freedom from rebound. The slowing down of the terminal phase of the opening movement also helps to ensure that the arc extinction air blast is allowed to act for a sufii cient time upon the arc andthe gases generated thereby, to purge the chamber completely.

A further object of the invention is to provide a circuit breaker of the above type in which means are provided to definea blast zone of invariable thickness; that is, one which does not change in size during the motion of the movable contact, and which hence can be designed to provide the optimum extinguishing eificiency.

Still another object of the invention is to provide a circuit breaker of the kind mentioned, and including a movable contact assembly provided with terminal motion damping means, such that the air pressure in the chamber during the opening movement is maintained more or less at the maximum level, for efiicient extinction, and until the moving contact has reached its maximum open position.

The above and other objects of the invention will best be understood by referring now to the following detailed specification of certain preferred and exemplary forms of the invention, taken in connection with the appended drawings, in which:

Fig. 1 is a vertical sectional view of the parts of an air blast circuit breaker essential to an understanding of the invention, the same having cylindrical symmetry.

Fig. 2 is a similar view of the lower portion of a modified circuit breaker, in which the moving contact is hollow so as to form a duct for the exhaust gases from the chamber.

Fig. 3 is also an axial vertical section of a circuit breaker wherein the moving contact withdraws through a blast orifice in the downward direction with respect to the orifice.

Fig. 4 is'again a similar view of the lower portion only of a modification related to the damping of the movement of the moving contact.

Electrical circuit breakers are known in which the 2,919,329 Patented Dec. 29, 1959 opening of the circuit, that is the separation of relatively movable contacts, is effected by a blast of compressed air which also operates to blow out the ionized gases which support the are formed when the opening of the circuit is initiated. Various objections have been noted in the operation of such breakers; for example, the initial rise of pressure in the breaker, when a circuit is to be opened, may be sufiicient to open the contacts slightly but insuflicient to extinguish the arc until a greater pressure has developed. This results in shortened life of the contacts and unreliable performance. The present invention overcomes this and othershortcomings of such previous designs.

Referring first to Fig. 1 of the drawings, there is shown a form of circuit breaker in accordance with the invention, and employing a hollow tubular fixed contact 4 through which the gases of the arc are expelled to the atmosphere, and a movable solid contact 1 cooperating therewith. Movable contact 1 is integral with a differential piston assembly comprising an upper piston 2 and a lower piston 3. The movable contact 1 cooperates with the fixed hollow contact 4 having the duct 5 through which the arcgases, as well as the extinguishing gases, are discharged to the open atmosphere. The two contacts may be of the pressure type, the pressure for holding them in contact being provided by a coil compression spring 6 urging the movable contact against the fixed contact. However, the contacts may also be of the friction type, one penetrating into the other, in which case spring 6 could be omitted.

In accordance with the invention, the smaller piston 3 of the differential piston operates within a cylinder 7 which communicates with the open atmosphere through an orifice 8 at its bottom, and with the arc extinction chamber (the interior of housing 13) through an orifice 9 in the side wall of the cylinder 7. The larger piston 2, which faces the movable contact 1, operates within a cylinder 10 communicating with the arc extinction chamber through orifices 11 in its side wall. A sliding contact 12 ensures a good conductive path from the metallic cylinder 10 to the movable contact 2. The cylinder 10 is connected through the metallic cylinder 7 to one terminal of the circuit breaker, the fixed contact being connected to the other terminal. The chamber housing 13 will ordinarily constitute the insulating envelope of the breaker, herein shown as ribbed in the known way to provide a longer leakage path for currents.

In operation, when the breaker is to be opened, compressed air from any suitable source is admitted to chamber 13, as indicated schematically via a duct passing through a control valve V which also may serve as a decompression valve for the chamber when the breaker is again to be closed. As the compressed air enters the chamber it penetrates through orifices 9 and 11 into the cylinders 10 and 7 and acts on the pistons 2 and 3. By proper choice of the number and size of these orifices, it can readily be arranged that the pressure developed upon piston 3 increases much more rapidly than that developed on the face of piston 2 directed toward the movable contact 1.

At this initial stage, then, the entry of the compressed air augments the pressure holding the contacts together. By choosing the proper size for the orifice 8, it can also be ensured that the pressure in cylinder 7 becomes stabilized much more rapidly than that in cylinder 10, so that the pressure on the upper face of piston z'continues to rise. Inasmuch as the piston 2 is the larger of the two, a point will be reached at which the force on 2 will exceed that on 3, and at this instant the assembly moves and the movable contact 1 will separate from fixed contact 4 and the opening movement begins.

This opening phase can be made very rapid by providing the supplementary orifices 14 in the side wall of cylinder 7, which are uncovered by the piston 2 early in its downward motion, thus allowing a large volume of compressed air to penetrate rapidly into cylinder to accelerate the remainder of the opening movement. Soon after the beginning of this opening movement, piston 3 closes orifice 9 and the air then within cylinder 7 is trapped and can only escape relatively slowly through exhaust orifice 8. The dash-pot action thus damps the final phase of the circuit opening movement, up to the point at which piston 3 reaches the bottom of cylinder 7 and bears against the sealing gasket 15. From this instant on, the lower surface of piston 3 is only subject to atmospheric pressure, while the upper surface of piston 2 is exposed to the pressure in the extinction chamber and the assembly remains stationary.

For this reason, the movable contact is readily maintained in its circuit open condition, against the action of spring 6 where such is employed, and even if the compressed air should leak into the space enclosed between the two pistons.

It will be realized that as soon as the separation of the contacts begins, the compressed air'supplied to the chamber begins to escape through the exhaust conduit 5. If desired, this conduit can be maintained closed by a suitable delay mechanism with a view to maintaining at least a residual pressure within the chamber 13.

Closure of the circuit breaker requires only that the chamber be returned to atmospheric pressure, as by operation of valve V to shut off the air supply and to vent the chamber to open air. The movable contact 2 will then return to the closed condition under the pressure of spring 6, and/or the action of the residual compressed air trapped between the pistons 2 and 3. If a very quick return of the piston is desired, the outflow of air from cylinder 10 can be accelerated by providing the upper wall of cylinder 10 with orifices 16 normally covered by a flap valve in the shape of a resilient washer 17. Also, orifices can be provided in the piston 2.

The location of the orifice 9 in the side wall of cylinder 7 can be varied according to the amount of damping desired. In particular, it is possible to place the orifice 9 at the bottom of the cylinder and to close it by a pressure check valve as described below in connection with Fig. 4 or" the drawings.

The invention can also be applied to circuit breakers in which the exhaust conduit is contained within the movable contact, rather than in the fixed contact, and such an arrangement is shown in Fig. 2 of the drawings, the contacts themselves being omitted in this showing. Here the same reference numerals are used to designate identical parts as in Fig. l, numeral 1 designating the tubular member which would carry the movable contact. The are gases can thus exhaust downward through this conduit and exit via orifices 18, flowing through the duct 19 and the exhaust orifice 20 into the outside atmosphere. The movable tubular contact is here integral with the differential piston again formed by the two pistons 2 and 3 which function as already described. The exhaust orifice 20 is arranged preferablyto be closed with a certain time delay by the valve 21, which is independent of the movable contact and is controlled by the pressure existing in chamber 13. The valve 21 is maintained in open position by the spring 22 which acts upon a piston 23 sliding in cylinder 24 and integral with the valve 21. The cylinder 24 communicates with the chamber 13, for example via the conduit 25.

This form of the invention operates as follows. Compressed air is again supplied through valve V to the chamber to initiate the opening movement. The movable contact rapidly separates from the fixed contact, causing a heavy inrush of air into the hollow contact. This air flows through the tubular conduit 1, orifices 18, conduit 19 and the exhaust orifice 20 into the free atmosphere. At the beginning of this flow, the closing valve 21 does not move, either because it is located in a cavity not reached by the airflow which urges it into closed position, or because it is retained by the spring 22. After a certain interval, predetermined by the dimensions of conduit 25 and the dead volume of the cylinder 24, a sufficient pressure is built up in the cylinder, which pushes the piston 23, and with it the valve 21, towards the left. As soon as the valve 2-1 has left its cavity, it is sucked by the strong exhaust flow and suddenly closes orifice 20. The breaker is therefore maintained open without substantial additional loss of compressed air. It is readily reclosed merely by exhausting the air pressure in the chamber 13, as by the decompression valve V.

Fig. 3 of the drawings illustrates a modified form of the invention in which the movable contact, again connected with the gas discharge conduit, cooperates with means defining a radial blast zone of fixed axial length, and hence operable efficiently regardless of the position to which the movable contact has moved during the opening movements. This form of the invention also provides a valve, integral with a moving contact assembly, for closing off the chamber from atmosphere after complete opening of the contacts (to maintain full or partial pressure in the chamber), and includes the motion damping and delaying features of the previously described embodiments.

In this figure, the movable contact 1 is formed at its contact end as a solid rod, fixed to one extremity of the tubular conduit 36 for the exhaust blast. This permits the use of very small arc blast orifice, but obviously the contact could be made hollow clear to its end if this size feature were not desired. The movable contact passes through at least one cylindrical cap 37 of insulating material having a rounded profile, and defining with fixed hollow contact 4 a radial blast zone of invariable thickness. The movable contact may also pass through a second cylindrical cap made of metal and operating as an arcing tip and electrostatic shield.

The compressed air, on admission, flows through the blast orifice in the cap 38 and thence through orifices 39, 40 and 41. The tube 36 carries the pistons 2 and 3 which again form a difierential piston. The exhaust valve 21 is fixed to the lower extremity of tube 36. The operation is similar to the species Figs. 1 and 2. However, when the extremity of the movable contact 1 has cleared the blast orifice of cap 37, the compressed air can flow freely through orifices 39, 40, 41 and 20 to the outside. After a very short interval, following parting of the contacts, the orifice 9 is closed by the piston 3 whereby the air beneath the piston is trapped, to damp the further motion of the contact tube.

As the position of the movable contact with respect to the blast orifice of cap 37, provided that the movable contact has completely cleared this orifice, has substantially no influence on the circuit-breaking power of the apparatus, it is possible to select the size of orifices 8 and 9, and the location of the latter, as well as the size and length of travel of the piston 3, so that the closing of the exhaust orifice 20 by the valve 21 occurs after a time suificient to allow the compressed air blast to exert its full action until completion of extinction of the are.

If it is desired to obtain a braking eifect from the moment of beginning of the motion of piston 3,- the orifice 9 may be placed, as shown in the modification of Fig 4, near the bottom of the cylinder within which the piston 3 moves, and provided with a check valve 42, arranged to prevent the return of the trapped air into the arc extinction chamber 13.

In the case where the movement of the movable contact is so greatly retarded that the build-up of counter-pressure between pistons 2 and 3 is to be feared, an orifice 43 (Fig. 3) may be provided to secure communication between the space enclosed between the pistons and the free atmosphere, until the movable contact has reached its fully open position.

While the invention has been described herein in considerable detail, by way of example and illustration, it will be appreciated by those skilled in the art that various changes in details may be efiected without departing from the spirit of the invention as defined in the appended claims.

What is claimed is:

1. In a circuit-breaker having a pair of normally closed contacts, one at least of which is axially movable and the movement of which is controlled by the pressure of an arc extinguishing gas admitted in to the arc extinction chamber and comprising pneumatic means responsive'to the initial admission of gas into said chamber, for pressing the contacts together to prevent premature separation thereof, the improvement which comprises a diiferential piston mounted on a movable one of said contacts, a dual chamber cylinder receiving said piston, and in which said opposite faces of said piston defines two chambers, the first chamber being so disposed that a rise of pressure in said first chamber upon admission of gas tends to cause said piston to move in the contact-opening direction, the second chamber being so disposed that a rise of pressure in said second chamber tends to cause said piston to move in the contact-closing direction, each of said first and second chambers having orifice means connecting respectively said first and second chambers with said are extinction chamber, said orifice means being so rated relatively one to the other that the pressure upon admission of pressure gas in said are extinction chamber rises more rapidly in said second chamber than in said first chamber whereby said piston presses the contacts together to prevent premature separation thereof.

2. A circuit-breaker in accordance with claim 1, in which said second chamber comprises supplementary orifice means connecting said second chamber to the atmosphere, said orifice means connecting respectively said first and second chambers to the are extinction chamber and said orifice means connecting said second chamber to the atmosphere being so rated relatively one to the other that the pressure upon admission of pressure gas in said are extinction chamber rises more rapidly in said second chamber than in said first chamber, whereby said piston presses the contacts together to prevent premature separation thereof.

3. A circuit-breaker in accordance with claim 1, in Which the orifice means connecting said second chamber with said are extinction chamber are so disposed as to form a gas trap in said second chamber, whereby the terminal movement of said piston in contact-opening direction is damped.

4. A circuit-breaker in accordance with claim 1, in which the orifice means connecting said first chamber .to said are extinction chamber comprises several orifices so disposed in spatial arrangement to be disclosed successively by said piston in its movement in contact-opening direction, whereby the movement of said piston is accelerated.

5. A circuit-breaker in accordance with claim 2, in which the piston includes, in said second chamber, aresilicut gasket positioned to serve as a stop for the motion of said piston, said orifice means connecting said second chamber to the atmosphere being so disposed as to be closed by said resilient gasket at the end of the contactopening movement of said piston.

6. A circuit-breaker in accordance with claim 2 in which at least one of said orifice means connecting said first chamber to said are extinction chamber is provided with exhaust flap, whereby the movement of said piston is accelerated in contact-closing direction.

7. A circuit-breaker in accordance with claim 3, in which guiding means for the air blast are provided delimiting a blast zone of predeterminated thickness and in which said orifice means connecting said second chamber with said are extinction chamber are disposed so as to be closed by said piston in its contact-opening movement when said blast zone is cleared by the contact, controlled by said piston whereby the damping action takes place without interference with the blast action.

8. A circuit-breaker in accordance with claim 1, in which the contact controlled by said piston is an hollow contact whereby the are extinction gases may escape to the atmosphere, exhaust orifice means connecting the inside of said hollow contact with the atmosphere being provided between said opposite faces of said piston.

9. A circuit-breaker in accordance with claim 8, in which said exhaust orifice means connect the inside of said hollow contact with the atmosphere through the intermediary of an exhaust chamber, said exhaust chamber including orifice means connected to the atmosphere and valve means controlling said last named orifice means, said valve means being controlled by means of the pressure in said are extinction chamber, whereby pressure gas is trapped in said are extinction chamber.

10. A circuit-breaker in accordance with claim 5, in which the contact controlled by said piston is an hollow contact whereby the extinction gases may escape to the atmosphere, exhaust orifice means connecting the inside of said hollow contactwith the atmosphere through said exhaust chamber, said exhaust chamber including orifice means connected to the atmosphere, said last named orifice means being disposed by means of said resilient gasket, whereby pressure gas is trapped in said are extinction chamber.

References Cited in the file of this patent UNITED STATES PATENTS 798,082 Sundh Aug. 29, 1905 2,592,079 Thommen et a1. Apr. 8, 1952 2,574,334 Latour Nov. 6, 1951 2,592,079 Thommen et a1. Apr. 8, 1952 2,747,055 Forwald May 22, 1956 FOREIGN PATENTS 319,277 Great Britain Sept. 18, 1930 335,380 Great Britain Sept. 25, 1930 432,453 Great Britain July 25, 1935 811,341 France Jan. 14, 1937 542,601 Great Britain Jan. 19, 1942 105,722 Sweden Oct. 20, 1942 

